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Hot rolled descaled steel coils - TDM

Our mechanical process for descaling hot rolled steel coils begins with powerful roller leveling that leaves the coil perfectly flat and free of residual tension. The material then passes through a series of abrasive rolls which remove rust and leave a carefully-controlled level of scale. Composed of wustite (FeO), this thin remaining layer, forms a natural protection against corrosion and gives improved smoothness and a clean outer appearance to the material. Water is used in a closed circuit to lubricate and clean the steel surface.
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The oxide layer is formed during the cooling phase in the hot rolling of steel coils. Consisting of hematite, magnetite, and wustite, the scale layer is about 0,5% of the total thickness of the steel sheet.
The wustite closest to the base metal substrate has a higher stability and lower oxygen content, and is therefore more resistant to corrosion.
After our mechanical descaling process, the thin remaining layer of wustite, from 8 to 20 microns thick, is firmly bonded to the steel base. This constitutes a natural protection against oxidation, and there is no need to oil the steel coils.

Qualities

DD11 - DD12
S235JR - S275JR - S355JR - S355J2+N
S355MC - S420MC - S500MC

All other qualities available on request up to a yield strength 700Mpa. Possibility of toll manufacturing.

Capacities

Coils up to 38 Mt
Thickness from 1 mm to 15 mm
Width up to 2100 mm


Advantages over Pickled and Oiled Material


• Longer shelf life, with no need to apply a protective layer of oil.
• Smooth, clean, and oil-free material means improved industrial processes such as laser cutting, welding, batch galvanization, and post painting.
• Parts and components obtained with TDM call for neither shot blasting nor degreasing before galvanizing or painting.
• Cleaner material means less dirt on equipment, tools and in storage areas.
• This ecological process avoids the use of acid, heating, and oiling for protective purposes.

Todoaceros provides descaled steel sheets that...

... are flat ...

Equipped with 11 working rolls, our roller leveler guarantees the flatness required for precise laser cutting and our double leveler system adapts the flatness according to the thickness of the sheets.

… have an improved surface …

Cleaner than classical pickled and oiled sheets, our TDM sheet surface is smoother and looks like a mill-finished cold sheet.

… are corrosion-resistant …

Our descaling process leaves a thin layer, from 8 to 20 microns of wustite (FeO) that is firmly bonded to the steel substrate. This naturally impedes oxidation and obviates the need for protective oil.

… require no protective oil …

The absence of oil on the steel sheets avoids toxic fumes during cutting, and parts need neither degreasing nor pre-treatment before painting or galvanizing. There is no suction effect between sheets while loading the material onto laser tables, which is particularly important with automatic loading systems.
Also, a clean and oil-free surface means less dirt in the storage area, working spaces, and on tools and equipment. .

… feature faster cutting speed ...

Excellent flatness combined with a smooth, clean, oil-free surface improves cutting speed by 10 to 30% compared with P&O material.

… are environmentally friendly.

An acid-free descaling process with no protective oil added constitutes Todoaceros’ commitment to provide products that respect the environment.
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Weld strength test of TDM sheets

This test realized in St Louis Testing Laboratories, Inc USA aims at comparing the quality and the resistance of welding between descaled and P&O sheets.

Test procedure

Five sets each of descaled material and P&O samples were prepared for spot welding. Samples consisted of two similar heavy gauge hot rolled panel overlapped and spot welded at the midpoint of the overlap. Each sample was vertically strained until rupture in a conventional tensile test machine.

Conclusion

1- The descaled material samples had an average failure shear load of 1573Kg, roughly 20% above P&O average.
2- Shear test indicate that weld integrity and fusion to base material is higher for descaled material that P&O hot rolled.
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Recommendations

GMAW / MIG
Filler Wire EN G3Sil / EN G4Sil between 0.8 and 1mm diameter.

Shielding gas: Argon / 3-5% Oxygen according to EN439M22 with a flow rate of 0.70 and 0.85 m3/h (25-30 CFH)

Wire speed and voltages:
10m/min 24 volts
11m/min 24 volts
12m/min 25 volts
13m/min 26 volts

The 95%Ar/5%O2 achieves spray arc mode, which minimizes spatter and produces a very uniform bead, allowing for a decreased wire feed speed. To avoid porosity from the O2 in the gas, the filler wire must have oxidizers. ENG3Sil and ENG4Sil has a high manganese content which serve this purpose.
GTAW / TIG
Filler rod: WT20 (red) according to EN 26848 with a diameter between 1.6 and 3.2mm according to sheets thickness.

Shielding gas: Argon with flow rate of 0.6 – 0.7 m3/h (15-20 CFH)

Amperage: 50-150A based on metal thickness

Voltage: 10-14 volts.

While MIG welding of carbon steels is preferable to TIG welding, mechanical discaled material does weld effectively because of its cleanliness. Areas to be welded must be free from moisture, oil and contaminants. A filler rod must be used to avoid porosity.
Resistance spot welding
Electrode: CuCr1Zr according to EN 12163 – cw106C pointed nose electrodes with a 16mm diameter.

Tip force: 2850 N +/- 150 N

Weld (Heat): 12,000 A +/- 300 A

Weld Time: 0,1 s / 0,2 s (5-10 Hz)

The electrical resistivity results show that descaled material has no more resistance to spot welding than does P&O and in fact has considerably less resistance than hot rolled black. Oxide pick-up when spot welding descaled material is considerably less than P&O and HRB.